Mobile computer systems have become a very popular form of computing device. Mobile computer systems allow users to access large amounts of personal information such as an address book, a personal calendar, and a list of to-dos. In particular, the PalmOS® based palm-sized computer systems that use the Palm Operating System from Palm Computing, Inc of Santa Clara, Calif. have become the de facto standard of handheld computer systems.
To provide additional functionality, it is desirable to include an external hardware interface on the mobile computer system. The Palm® series of palm-sized computer systems from Palm Computing, Inc of Santa Clara, Calif. include an external serial interface for communicating with external peripherals. The Handspring® line of Visor® palm-sized computer systems include a Springboard® expansion port that allows even more sophisticated peripherals to be added.
There are few limits on the types of peripherals that peripheral designers may create for palm-sized computer systems. Currently available peripherals for palm-sized computer systems include Global Positioning System (GPS) receivers, MPEG audio layer 3 (MP3) players, barcode laser scanners, cellular modems, ordinary telephone line modems, cellular telephones, digital cameras, flash memory storage, and software read-only-memory (ROM) packs.
To allow peripheral designers as much freedom as possible, it would be desirable to provide the peripheral designers with as many computer resources as possible without rendering the palm-sized computer system impractical. One common need of most computer peripherals is electrical power. Thus, it would be desirable to provide peripheral designers with ample electrical power. However, the electrical power must be supplied without harming the ordinary operation of the palm-sized computer system.